Magnetic Resonance Imaging of Gliomas

Open Access.This work was supported in part by grants CTQ2010-20960-C02-02 to P.L.L. and grant SAF2008-01327 to S.C. A.M.M. held an Erasmus Fellowship from Coimbra University and E.C.C. a predoctoral CSIC contract.Peer Reviewe

Arterial Spin Labeling Perfusion of the Brain: Emerging Clinical Applications

Arterial spin labeling (ASL) is a magnetic resonance (MR) imaging technique used to assess cerebral blood flow noninvasively by magnetically labeling inflowing blood. In this article, the main labeling techniques, notably pulsed and pseudocontinuous ASL, as well as emerging clinical applications will be reviewed. In dementia, the pattern of hypoperfusion on ASL images closely matches the established patterns of hypometabolism on fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) images due to the close coupling of perfusion and metabolism in the brain. This suggests that ASL might be considered as an alternative for FDG, reserving PET to be used for the molecular disease-specific amyloid and tau tracers. In stroke, ASL can be used to assess perfusion alterations both in the acute and the chronic phase. In arteriovenous malformations and dural arteriovenous fistulas, ASL is very sensitive to detect even small degrees of shunting. In epilepsy, ASL can be used to assess the epileptogenic focus, both in peri- and interictal period. In neoplasms, ASL is of particular interest in cases in which gadolinium-based perfusion is contraindicated (eg, allergy, renal impairment) and holds promise in differentiating tumor progression from benign causes of enhancement. Finally, various neurologic and psychiatric diseases including mild traumatic brain injury or posttraumatic stress disorder display alterations on ASL images in the absence of visualized structural changes. In the final part, current limitations and future developments of ASL techniques to improve clinical applicability, such as multiple inversion time ASL sequences to assess alterations of transit time, reproducibility and quantification of cerebral blood flow, and to measure cerebrovascular reserve, will be reviewed

상이한 상용 소프트웨어를 사용한 CT 관류 맵에서의 경색 용적 측정: 급성 뇌졸중 환자에서 동일한 소스 데이터를 사용한 정량적 분석

학위논문(석사) -- 서울대학교대학원 : 의과대학 의학과, 2021.8. 손철호 .연구 목적: CT 관류 영상 (CT Perfusion map, CTP) 급성 허혈성 뇌졸중 환자의 치료 여부의 선택 결정과정에 실제로 널리 사용되고 있지만, 정확한 경색 중심부 용적을 예측하는 데 사용되는 최적의 임계값과 매개 변수에 대해서는 명확한 표준이 없다. 현재 rCBF <30 %의 임계값을 가진 경색 중심부(Infarct core) 용적이 일반적으로 사용되고 있다. 그러나 Follow-up diffusion-weighted imaging (DWI)와 경색 중심부(Infarct core) 용적의 일치를 평가하기 위해 CTP와 DWI 사이의 시간간격이 24 시간 이내인 여러 연구가 진행되었다. 본 연구의 목적은 RAPID, singular value decomposition+ (SVD+) VITREA, BAYESIAN VITREA 등의 CTP 소프트웨어 프로그램에서 다양한 Deconvolution 방법, 매개 변수, 임계값에 따라 측정된 경색 중심부 용적과 짧은 시간 간격으로 (60분 이내) 시행된 DWI에서 측정된 경색 중심부용적과의 일치율을 평가한다. 연구 방법: 전방 순환에 있어서 큰 혈관의 폐색증을 가진 42명의 급성 허혈성 뇌졸중 환자가 포함되었다. CT 관류 영상은 VITREA 및 RAPID의 SVD +와 Bayesian 알고리즘을 포함한 다양한 CT 관류 소프트웨어로 처리되었다. RAPID는 경색 중심부를 rCBF <20 % -38 %, rCBV <34 % -42 %을 가진 조직으로 식별하였다. SVD+ VITREA에서는 경색 중심부를 CBV의 26-56 % 감소로 정의하였다. BAYESIAN VITREA에서는 경색 중심부를 CBV의 28-48% 감소로 정의하였다. Olea Sphere는 DWI 경색 중심부 용적을 측정하는 데 사용되었다. CTP 중심부 용적의 측정값은 DWI에서 결정된 최종 경색 용적과 비교되었다. 연구 결과: CTP는 모든 환자에서 DWI 전에 실시되었고, CTP와 DWI 사이의 시간의 중앙값은 37.5 분(min)이었다 interquartile range (IQR) 20 -44. 42 명의 환자에서는 최종 경색 중심부 용적의 중앙값은 DWI에서 19.50 ml (IQR 6.91 - 69.72) 였다. RAPID rCBF <30% 기본 설정값에서 경색 중심부 용적 차이의 중앙값은 (IQR) 8.19 ml (3.95 – 30.70), spearman’s correlation coefficient (r) = 0.759를 얻을 수 있었으며; SVD+ VITREA CBV의 41% 감소 시 경색 중심부 용적 차이의 중앙값은 (IQR) 3.82 ml (-2.91 – 20.95), r = 0.717로, BAYESIAN VITREA CBV의 38% 감소 시 경색 중심부 용적 차이의 중앙값은 (IQR) 8.16 ml (1.58 – 25.46), r = 0.754이었다. 반면 각 소프트웨어에 대한 최적의 임계값은 경색 중심부 용적을 기본 설정보다 정확하게 추정하는 것으로 입증되었다. 각 소프트웨어의 가장 정확하고 최적의 경색 중심부 용적 차이의 임계값은 다음과 같았다: RAPID rCBF <38 % 경색 중심부 용적 차이는 4.87 ml (0.84 – 23.51), r = 0.752; SVD + VITREA CBV이 26 % 감소 시 경색 중심부 용적의 용적 차이가 -1.05 ml (-12.26 – 14.58), r = 0.679로 나타났으며; BAYESIAN VITREA CBV의 28 % 감소는 경색 중심부 용적 차이가 5.23 ml (-2.90 – 22.91), r = 0.685였다. 결론: 본 연구에서는 CBV 임계값은 CBF 임계값과 비교하여 급성 허혈성 뇌졸중 환자의 경색 중심부 용적을 예측하는 더 정확한 매개 변수를 제공하는 것으로 나타났다.Purpose: Although using Computed Tomography Perfusion (CTP) for selecting and guiding decision-making processes of a patient with acute ischemic stroke has its advantages, there is no clear standardization of the optimal threshold and parameters used to predict infarct core volume accurately. Nowadays, infarct core volume with a rCBF<30% threshold is commonly used. However, several studies have been performed to assess the volumetric agreement of CTP infarct core volume with follow-up Diffusion-Weighted Imaging (DWI); the time between CTP and DWI was within 24 hours. In this study, we aimed to assess the volumetric agreement of estimated infarct core volume with different deconvolution methods, parameters, and thresholds on CTP software programs, including: RAPID, singular value decomposition plus (SVD+) VITREA, BAYESIAN VITREA, and also the final infarct volume on DWI with an especially short interval time (within 60 min) between CTP and follow-up DWI. Materials and methods: Forty-two acute ischemic stroke patients with occlusion of a large artery in the anterior circulation were included in the study. The CT perfusion maps were processed with different CT perfusion software, including SVD+ and Bayesian algorithms in VITREA and RAPID. The RAPID identified infarct core as tissue rCBF < 20-38% and rCBV < 34-42%. The SVD+ VITREA defined infarct core as CBV reduction of 26% - 56%. The Bayesian VITREA quantified infarct core as tissue CBV reduction of 28% - 48%. Olea Sphere was used to measure the infarct core volume on DWI. The CTP infarct core volume measurements were compared with the final infarct volume, which was determined on DWI. Results: The CTP was performed before DWI in all patients, and the median time between CTP and DWI was 37.5 minutes, with an interquartile range (IQR) of 20 – 44. In 42 patients, the median final infarct volume was 19.50 ml (IQR 6.91 – 69.72) with DWI. The most commonly used thresholds for each kind of CTP software, including RAPID rCBF<30%, resulted in a median infarct volume difference (IQR) of 8.19 ml (3.95 – 30.70), spearman’s correlation coefficient (r) = 0.759; SVD+ VITREA CBV reduction of 41% demonstrated a median infarct volume difference (IQR) of 3.82 ml (-2.91 – 20.95), r = 0.717; and BAYESIAN VITREA CBV reduction of 38% resulted in a median infarct volume difference (IQR) of 8.16 ml (1.58 – 25.46), r = 0.754. On the other hand, the optimal thresholds for each kind of software ended up estimating infarct core volume more accurately than the commonly used thresholds with lower infarct core volume differences. The most accurate and optimal infarct core volume thresholds for each kind of software were as follows: median infarct core volume difference (IQR) for RAPID rCBF<38% was 4.87 ml (0.84 – 23.51), r = 0.752; SVD+ VITREA CBV reduction of 26% was -1.05 ml (-12.26 – 14.58), r = 0.679; BAYESIAN VITREA CBV reduction of 28% was 5.23 ml (-2.90 – 22.91), r = 0.685. Conclusions: Our study found that the CBV thresholds provide a more accurate parameter to predict infarct core volume in acute ischemic stroke patients compared with the CBF thresholds.Chapter 1. Introduction 1 Chapter 2. Materials and methods 13 Chapter 3. Results 18 Chapter 4. Discussions 57 Chapter 5. Conclusions 64 Bibliography 65 Abstract in Korean 71석

Regional Low Cerebral Blood Flow Predicts Leukoaraiosis Development at 18 Months in Patients with TIA and Minor Stroke

The purpose of this study was to investigate whether low cerebral blood flow (CBF) is associated with subsequent white matter hyperintensity (WMH) development in minor stroke and transient ischemic attack (TIA) patients. New WMH at 18 months were identified by comparing follow-up with baseline FLAIR, and regions of interest (ROI) were placed in normal appearing and hyperintense white matter. Co-registered CBF maps were used to quantify relative CBF. Forty patients were evaluated, where mean age was 62+/-12 years, 78% male and 9% diabetic. A mixed effects logistic regression accounting for “within patient” clustering, showed that as CBF increases by 1mL/100g/min, the odds of having a new WMH decrease by 0.61. Results suggest that regions of white matter that develop WMH at 18 months have low baseline CBF. Future studies aiming to improve cerebral perfusion in normal appearing white matter might provide a target for arresting the development of WMH

Cerebral blood perfusion changes in multiple sclerosis

The proximity of immune cell aggregations to the vasculature is a hallmark of multiple sclerosis. Furthermore, it is widely accepted that inflammation is able to modulate the microcirculation. Until recently, the detection of cerebral blood perfusion changes was technically challenging, and perfusion studies in multiple sclerosis patients yielded contradictory results. However, new developments in fast magnetic resonance imaging have enabled us to image the cerebral hemodynamics based on the dynamic tracking of a bolus of paramagnetic contrast agents (dynamic susceptibility contrast). This review discusses the technical principles, possible pitfalls, and potential for absolute quantification of cerebral blood volume and flow in a clinical setting. It also outlines recent findings on inflammation associated perfusion changes, which are inseparable from pathological considerations in multiple sclerosis

Applications of CT Perfusion-Based Triaging and Prognostication in Acute Ischemic Stroke

CT Perfusion (CTP) is a minimally invasive imaging technique that aids acute ischemic stroke (AIS) triage and prognostication by determining tissue viability based on hemodynamic parameters. The goals of this research are to determine: 1) CTP thresholds for estimation of infarct and penumbra volume, 2) how CTP scan duration impacts infarct and penumbra volume estimates, and 3) reliability of CTP for predicting functional outcomes following intra-arterial therapy (IAT). Chapter 2 introduced an experimental study for determining ischemia-time dependent thresholds for brain infarction using multimodal imaging in a porcine stroke model that is easier to implement than previous large animal stroke models. CTP determined an absolute cerebral blood flow (CBF) threshold of 12.6±2.8mL∙min-1∙100g-1 for brain infarction after 3h of ischemia, which was close to that derived using hydrogen clearance in a previous study by Jones et al (Journal of Neurosurgery, 1981;54(6):773-782). Chapter 3 retrospectively investigated the impact of CTP scan duration on cerebral blood volume (CBV), CBF, and time-to-maximum (Tmax) and found optimal scan durations that minimized radiation dose while not under- or over-estimating infarct volumes measured using two previously derived CBF thresholds for infarction. We found that CBV and Tmax decreased at shorter scan durations, whereas CBF was independent of scan duration, consequently, infarct volume estimated by both CBF thresholds was independent of scan duration. Chapter 4 compared reperfusion seen on follow-up CTP to reperfusion predicted by post-IAT digital subtraction angiography (DSA) and the ability of the two modalities to predict good 90-day functional outcome in a retrospective study. We found that patients with ‘complete reperfusion’ grades on DSA often had ischemic tissue on follow-up CTP and that follow-up CTP had superior specificity and accuracy for predicting functional outcome compared to DSA. In summary, this research has shown that CBF thresholds can reliably detect infarct in AIS and are independent of scan duration, allowing radiation dose to be minimized by limiting scans to 40s without compromising accuracy of infarct volume estimates. Finally, CTP is a more specific and accurate predictor of functional outcome than the commonly used post-procedural DSA, this could help select patients for neuroprotective therapy